It is known to test high-pressure lines, in particular also metal high-pressure lines for a fuel injection system, for manufacturing or material flaws by means of pressurization. In the process, the pipes are usually pressurized with a pressure above the actual operating pressure, under provisions regarding pressure increase and retention time of the testing pressure, in order to carry out a reject test. As is known, this test is deficient because it does not enable any information about the inner structure of the pipes. Structural flaws in the inner structure of the pipes, which may not lead to an acute failure of the pipes, but which nevertheless constitute a risk of future failure, are not recognized in this way. Attempts for inspecting the pipes in a non-destructive and volume-oriented manner made so far failed because of the costs, with respect to the usual radiography-based inspections.
On the other hand, and in particular where ultrasound was concerned, the prejudice prevailed with regard to these high-pressure lines, which, compared to the usual test specimens for ultrasonic testing, generally had small dimensions, that ultrasound was not suitable, due to the comparatively large dimensions of the sound transducers, and could not be coupled in in a reproducible manner for the purpose of an inspection. In addition, there is the problem, as a rule, that these pipes are not configured in a straight line, so that the usual approaches such as those that are customary in the inspection of gas or oil pipelines, and which provide, for example, an irradiation angled in circumferential direction of the tube in order to cause a sound propagation in the circumferential direction, fail in the inspection of high-pressure lines because the required angle for the defined angled emission of the ultrasonic transducer into the test piece cannot be maintained, or at least not reproducibly.